The glutenins, which include both high molecular weight (HMW) glutenin subunits and low molecular weight (LMW) glutenin subunits, comprise an economically important class of wheat seed storage proteins. The apparent molecular weights of the individual HMW glutenin polypeptides or subunits range from 90 to 200 kDa. These subunits crosslink by disulfide bonds among themselves and with LMW glutenin polypeptides to form polymers exceeding one million daltons in molecular weight. HMW glutenins constitute 8-10%, while LMW glutenins constitute 15-20% of the total endosperm protein. Both HMW and LMW glutenin proteins play important functional roles in determining the end-uses of wheat flour.
In wheat, HMW glutenins are encoded at the Glu-1 loci on the long arms of the group 1 chromosomes. Each locus consists of two separate genes, encoding an x-type and a y-type subunit, respectively. These pairs have never been confirmed to be separated by recombination. This has made determination of their separate contributions to bread dough properties difficult to assess by genetic correlation studies. For a review of the genetics and biochemistry of glutenin polypeptides, see, Shewry et al., J. Cereal Sci. 15:105-120 (1992).
Both the quantity and identity of specific HMW glutenin alleles contribute to the differences in bread-making quality of various cultivars. For instance, deletion of glutenin genes results in a decrease in the overall levels of HMW glutenins, which results in decreases in bread-making quality (see, e.g., Lawrence et al. J. Cereal Sci 7:109-112 (1988)).
The effects of overproducing HMW glutenin on protein accumulation and baking quality has not been assessed because such lines of wheat have not been found among natural populations. In addition, direct alteration of the glutenin subunits that form the polymers is not possible using standard breeding methods. Thus, the art lacks reproducible and efficient methods of producing lines with altered glutenin contents. The present invention addresses these and other needs.